杭电ACM1071The area---------求积分面积

 #include <iostream>
 #include <stdio.h>
 using namespace std;
 int main()
 {   int t;
     double x1,y1,x2,y2,x3,y3,a,k,s;
     cin>>t;
     while(t--)
     { cin>>x1>>y1>>x2>>y2>>x3>>y3;
       a=(y2-y1)/((x2-x1)*(x2-x1));
       k=(y2-y3)/(x2-x3);
       s=a/3*(x3*x3*x3-x2*x2*x2)+(a*x1*x1+k*x3+y1-y3)*(x3-x2)+0.5*(2*a*x1+k)*(x2*x2-x3*x3);
        printf("%.2f\n",s);
     }
 return 0;
 }